Here is a bit of additional information on the LiFePO4 packs we'll be carrying. These are packs made specifically for electric bikes by PHET (Phisiang Industries) that make the highest quality C-coated lithium iron phosphate (C-LiFePO4) cells available, based on the Phostech chemistry. For pictures of the packs, see
We have been testing the pack for about two weeks now, on our Xtracycle/Currie USPD high-power drive setup (600W+).
At an average 1C rate, the pack does appear to have the rated capacity of 7.5AH. This is just enough for a 15 mile trip with the loaded Xtracycle, in our moderately hilly area. When the pack voltage drops to about 25V, the battery management system will turn it off temporarily until voltage recovers.
The voltage curve on these is flat. They stay above 36V until about 7.1~7.2 AH of use. This is really nice in comparison to a lead acid, it allows use of nearly all the battery capacity. There is more information on the PHET batteries
.
The charger is built very solidly. We haven't measured the efficiency yet, but we will do so and post here.
Earlier, we posted that there was a current limit at 20A. Based on conversations with the manufacturer and our own further testing, this isn't true. Instead, the BMS system is set up so that if cell voltage drops below around 2.5V/cell (maybe a bit less) it cuts out power for a few seconds until the voltage recovers. The only time this seems to happen is when we are accelerating uphill on the Xtracycle/Currie/BMC setup, which can easily drain 30A. We've tested at a relatively constant 20A current for 1 minute or more, and it doesn't seem to cut out.
About the only negative so far about this pack is that the plastic handle on the end is a bit flimsy. It is solid enough for carrying the battery, but we cracked ours when we dropped the pack on it from a few inches height. A bit of duct tape fixed that right up!
All in all, this is a solid performing pack! We don't use our NiMH or SLA packs anymore (
The charger is built very solidly. We haven't measured the efficiency yet, but we will do so and post here.
Earlier, we posted that there was a current limit at 20A. Based on conversations with the manufacturer and our own further testing, this isn't true. Instead, the BMS system is set up so that if cell voltage drops below around 2.5V/cell (maybe a bit less) it cuts out power for a few seconds until the voltage recovers. The only time this seems to happen is when we are accelerating uphill on the Xtracycle/Currie/BMC setup, which can easily drain 30A. We've tested at a relatively constant 20A current for 1 minute or more, and it doesn't seem to cut out.
About the only negative so far about this pack is that the plastic handle on the end is a bit flimsy. It is solid enough for carrying the battery, but we cracked ours when we dropped the pack on it from a few inches height. A bit of duct tape fixed that right up!
All in all, this is a solid performing pack! We don't use our NiMH or SLA packs anymore (
if you want to buy a lightly used SLA or NiMH pack in a nice case).
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